Getting Started with Claude Code

pip install anthropic

import anthropic
import os

# The anthropic library automatically uses the ANTHROPIC_API_KEY environment variable.
# If you haven't set it, you can uncomment the line below and paste your key directly,
# but this is NOT recommended for security reasons.
# client = anthropic.Anthropic(api_key="YOUR_ANTHROPIC_API_KEY")

client = anthropic.Anthropic() # Reads API key from ANTHROPIC_API_KEY environment variable

try:
    message = client.messages.create(
        model="claude-3-opus-20240229", # Or another Claude 3 model like "claude-3-sonnet-20240229"
        max_tokens=1000,
        messages=[
            {
                "role": "user",
                "content": "Write a simple Python function to add two numbers."
            }
        ]
    )
    print(message.content)

except anthropic.APIConnectionError as e:
    print("The server could not be reached")
    print(e.__cause__)  # an underlying Exception, likely `requests.exceptions.Timeout`
except anthropic.RateLimitError as e:
    print("A 429 status code was received; we should back off")
    print(e)
except anthropic.AuthenticationError as e:
    print("Authentication failed. Check your API key.")
    print(e)
except anthropic.APIStatusError as e:
    print(f"An API error occurred: {e.status_code}")
    print(e.response)
except Exception as e:
    print(f"An unexpected error occurred: {e}")

Here's a simple Python function to add two numbers:

```python
def add_numbers(a, b):
  """
  This function takes two numbers as input and returns their sum.

  Args:
    a: The first number.
    b: The second number.

  Returns:
    The sum of a and b.
  """
  return a + b

# Example usage:
# result = add_numbers(5, 3)
# print(result)  # Output: 8

## 3) Common Mistakes

*   **Not setting the `ANTHROPIC_API_KEY` environment variable:** The `anthropic` library will fail to authenticate if it cannot find your API key.
*   **Using an invalid API key:** Ensure you have copied the key correctly and that it hasn't expired or been revoked.
*   **Incorrectly specifying the model:** Ensure you are using a valid and available Claude model name (e.g., `claude-3-opus-20240229`).
*   **Exceeding `max_tokens`:** If your prompt or Claude's response is too long, you might encounter errors. Adjust `max_tokens` accordingly.
*   **Typos in the `messages` structure:** The `role` and `content` keys must be correctly formatted.

## 4) Troubleshooting

*   **`AuthenticationError`:**
    *   **Cause:** Invalid or missing API key.
    *   **Solution:** Double-check that your `ANTHROPIC_API_KEY` environment variable is set correctly and contains your actual API key. Regenerate the key from your Anthropic account if necessary.
*   **`APIConnectionError`:**
    *   **Cause:** Network issues preventing your script from reaching Anthropic's servers.
    *   **Solution:** Check your internet connection. Ensure no firewalls are blocking outgoing requests to `api.anthropic.com`. Try pinging the domain.
*   **`RateLimitError`:**
    *   **Cause:** You have made too many requests in a short period, exceeding your API rate limits.
    *   **Solution:** Implement exponential backoff in your application or wait for a period before retrying. Check your usage dashboard for current limits.
*   **Empty or unexpected response:**
    *   **Cause:** The prompt might be too ambiguous, or the model might not have understood the request.
    *   **Solution:** Refine your prompt to be more specific. Try a different phrasing. Ensure you are using a capable model for the task.

## 5) Final Checklist

*   [ ] Anthropic account created and accessible.
*   [ ] API key generated and securely stored.
*   [ ] `anthropic` Python library installed (`pip install anthropic`).
*   [ ] `ANTHROPIC_API_KEY` environment variable correctly set and active.
*   [ ] Test script runs without errors and produces expected output.
*   [ ] You understand the basic structure of sending messages to the API.

## 6) FAQ

**Q1: How do I choose the right Claude model?**
**A1:** Anthropic offers different Claude 3 models (e.g., Opus, Sonnet, Haiku) with varying capabilities and costs. Opus is the most powerful but also the most expensive. Sonnet offers a balance of performance and cost, while Haiku is the fastest and most affordable. For general coding tasks, Sonnet is often a good starting point. Refer to the [Anthropic documentation](https://docs.anthropic.com/claude/docs/models-overview) for detailed comparisons.

**Q2: Can I use Claude Code without Python?**
**A2:** While this guide focuses on the Python SDK, Anthropic's API can be accessed via direct HTTP requests. This means you can integrate Claude into applications written in any language that can make web requests. However, the Python SDK simplifies many aspects of the interaction.

**Q3: What are the costs associated with using Claude Code?**
**A3:** Usage of the Claude API is priced based on the model used and the number of tokens processed (both input and output). You can find the current pricing details on the [Anthropic pricing page](https://www.anthropic.com/pricing). It's advisable to monitor your usage through your Anthropic account dashboard.

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